Table 2.

Major Inborn Errors of Metabolism Presenting in the Neonate as an Acute Encephalopathy

DisordersCharacteristic Laboratory FindingsReferences
Organic acidemias (includes MMA, PA, IVA, MCD and many less common conditions)Metabolic acidosis with increased anion gap; elevated plasma and urine ketones; variably elevated plasma ammonia and lactate; abnormal urine organic acids6–8
Urea cycle defectsVariable respiratory alkalosis; no metabolic acidosis; markedly elevated plasma ammonia; elevated orotic acid in OTCD; abnormal plasma amino acids9
Maple syrup urine diseaseMetabolic acidosis with increased anion gap; elevated plasma and urine ketones; positive ferric chloride test; abnormal plasma amino acids10
Nonketotic hyperglycinemiaNo acid-base or electrolyte abnormalities; normal ammonia; abnormal plasma amino acids11
Molybdenum co-factor deficiencyNo acid-base or electrolyte abnormalities; normal ammonia; normal amino and organic acids; low serum uric acid; elevated sulfites in urine12
  • Abbreviations: MMA, methylmalonic acidemia; PA, propionic acidemia; IVA, isovaleric acidemia; MCD, multiple carboxylase deficiency; OTCD, ornithine transcarbamylase deficiency.